m68k: define a local gpio_request_one() function

Compiling for linux-3.9-rc1 and later fails with:

drivers/gpio/devres.c: In function 'devm_gpio_request_one':
drivers/gpio/devres.c:90:2: error: implicit declaration of function 'gpio_request_one' [-Werror=implicit-function-declaration]

So provide a local gpio_request_one() function. Code largely borrowed from
blackfin's local gpio_request_one() function.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>